Add `token` field to `payment_received` event data

[Kingsman-99]

Description

payment_received in contracts/split/src/events.rs emits (payer, amount, event_seq) but omits the token address. For multi-token invoices this makes off-chain reconciliation ambiguous. Adding token: &Address to the data tuple would allow indexers to distinguish XLM from USDC payments without a separate lookup.

Acceptance Criteria

• Update payment_received(env, invoice_id, payer, amount) signature to add a token: &Address parameter
• Include token in the published event data: (payer, amount, token, event_seq)
• Update all call sites in contracts/split/src/lib.rs
• Update tests that assert the event data shape
• cargo test passes

Context

• Target file: contracts/split/src/events.rs, call sites in contracts/split/src/lib.rs

[Teejay2696]

@Teejay2696 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Let me wok on this issue Asap

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[Onomebello]

@Onomebello has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

please assign me this issues

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Third Campaign campaign!

@Onomebello's PR #727 was approved and merged by @Kingsman-99.

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👏 Great work, @Onomebello! Keep contributing to Stellar-split.

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This issue has been completed by @Onomebello as part of the Stellar Wave Program's 8th Wave 🥳

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